Underwater communication and control



UNDERWATER COMMUNICATION AND CONTROL Filed Feb. 12, 1964 4 Sheets-Sheet 1 TIME FIGJ

PRESSURE NOV. 17, 1970 5. r m ETAL UNDERWATER COMMUNICATION AND CONTROL 4 Sheets-Sheet 2 Filed Feb. 12.- 1964 Im qmb N QE 1.3250104 NI A 9 2+ Nov 17,1970 5. EPSTEIN a'rAl. 3,541,500

UNDERWATER COMMUNICATION AND CONTROL- Feb. 12. 1964 4' Sheets-$heet 3 Filed lxlo o"= H (BOTI'O M) FMUkO i! Z- IFlwD dfrikmOmofI N WQLQXIO"? (SURFACE TlME IN MiLLlsECC'lflDs FIG.3

United States Patent Ofi ice 3,541,500 Patented Nov. 17, 1970 3,541,500 UNDERWATER COMMUNICATION AND CONTROL Sidney Epstein and David Epstein, Brooklyn, N.Y., as-

signors to Vadys Associates, Ltd., Brooklyn, N.Y., a

corporation of New York Filed Feb. 12, 1964, Ser. No. 344,491 Int. Cl. H041) 11/00 U.S. Cl. 340-5 3 Claims This invention generally relates to an underwater explosive signalling or communication and control system.

Prior art underwater explosive signalling systems typically use an explosive transmitter consisting ofa plurality of explosive charges which are fired in a predetermined time sequence; this time sequence constitutes a coded message. By varying the time between charge detonations, a number of temporal charge detonation pattern combinations are obtained; each one of these combinations is put into one-to-one correspondence with a specific message. The receiver(s) typically contain means to detect explosive signals, decode the signals, and apparatus to act upon the message content. The decoder would ordinarily operate in the time or frequency domains. One such system is described in Sound, 2, No. 1, p. 60 (1963).

All such prior art systems use a plurality of charges (excluding the trivial case wherein meaning is assigned to the presence or absence of an explosion or the impractical case wherein an attempt is made to set up a one-toone correspondence between different explosive charge magnitudes and different messages). In practice, it is usually found that the larger the required vocabulary (the totality of unique messages), the greater the number of charges required. The size, complexity, and cost of multiple, sequential, explosive transmitters (i.e., the multiple explosive transducer, the primer detonation electrical equipment, electrical cabling, electronic timer, etc.) are proportionate to the number of explosive charges involved.

It is an object of this invention to provide a simpler and more economic underwater signalling system using a single explosive charge per message.

Another object is to provide a large set of unique messages (vocabulary) for the system.

Still another object of this invention is to provide an expendable explosive-charge/hydrostatic-fuze transmitter unit for the single charge per message underwater explosive signalling system. The transmitter ordinarily consists of the explosive charge, a presettable-pressure hydrostaticfuze, and a gravitational sinker. The desired message is selectively coded in accordance with a preordained message/depth dictionary. The receiver(s) decode the message in either the time or frequency domain in accordance with well known statistical communication techniques, e.g., correlation, filtering, hypothesis testing, adaption, etc.

A feature of this invention is the utilization of the bubble pulse phenomenon characteristic of an underwater explosion for system operation. An explosive charge detonated under water yields the general waveform shown in FIG. 1; the main pressure peak 7 is followed by a series of secondary peaks of rapidly diminishing amplitude, referred to as bubble pulses. The period of the first, or strongest bubble pulse 9 is given, by D. E. Weston, Proc. Phys. Soc. (London), 76, p. 233 (1960), with good accuracy by the equation: T =kw z seconds; where T is the first bubble pulse period, k is a parameter which equals 4.36 for TNT, w is the weight of the explosive charge in pounds, and z is the hydrostatic depth in feet (the actual physical depth plus 33 ft.). It is clear from the equation for T that for a given type and weight of charge, the firing depth uniquely determines the period T thus a one-to-one correspondence exists between the firing depth, z, and said time interval, T intermediate the main pressure peak and the first bubble pulse. The sensing of said time interval represents decoding in the time domain, the presently preferred method of decoding the messages; alternately, decoding may take place in the frequency domain because of the corresponding uniqueness of the frequency spectrum of the explosive waveform due to the interference between the main pressure peak and the first bubble pulse. Consequently, if a symbol, wordcommand, or message is associated with the particular firing depth, then the range of ocean depths provides a large vocabulary for the message/ depth dictionary. The actual realizible size of the vocabulary is limited by the water depth in the particular transmission area, the accuracy of the equation for T the accuracy and resolution of the electronic equipment used to measure T in the time domain or its dual in the frequency domain, the dynamic range accuracy and resolution of th pressure detonating mechanism, the seriousness of multi-path interference due to surface and bottom reflections, and the sound conditions.

The abovementioned and other features and objects of the invention will become more apparent from the following specification and claims and from the accompanying drawings which illustrate the principles of the invention as incorporated in presently preferred embodiments thereof.

Referring to the figues:

FIG. 1 shows a representative pressure vs. time diagram for a deep-fired explosion.

FIG. 2 illustrates schematically an idealized signalling system following the principles of the subject invention.

FIG. 3 shows bubble pulse period vs. hydrostatic depth with charge weight as parameter. Superimposed are curves giving time of occurrence of first surface reflected shock wave pulse vs. depth for certain values of receiver range x and depth y.

FIG. 4 is a schematic block diagram which illustrates a presently preferred embodiment of a portable and expendable explosive transmitter package.

FIG. 5 is a schematic block diagram which illustrates a presently preferred embodiment of an explosive shock wave receiver package.

FIG. 6 is a block diagram which illustrates the receiving, amplifying, detecting, decision making, decoding, and error-correcting aspects of the presently preferred embodiment of the explosive shock wave receiver.

FIGS. 2, 4 and 5 comprise a one-way signalling system, however, by providing the transmitting station with a receiver and the receiving stations with explosive transmitters, two-way signalling is readily obtainable.

Referring to FIG. 2, a receiving station 6 can, in the general case, be anywhere in the ocean at horizontal range, x, at any depth, y, and explosive detonation may take place at any depth, 2; both y and z are constrained to lie between the surface and the bottom, z=H, of the ocean. For illustrative purposes, H has been arbitrarily set at 15 kilofeet. If, for the sake of illustration, a twoounce weight of TNT is used as the explosive charge, rapid calculation shows that line 1 of FIG. 3 represents the functional relationship of T vs. z; it is seen that T lies in the interval from 0.7 to milliseconds. This fact implies that surface and bottom reflections, which for certain combinations of the variables x, y, z, will appear within this interval, may strongly interfere with the signalling process. While to fully discriminate between the desired signal and the multipath interference may require some receiver sophistication, there are limited communication regions, i.e., x and y confined to a region bounded by (x x and (y y' respectively, where it can be shown that no reflected pulses will appear within the T interval if some regions along z are excluded. This allows an unsophisticated receiver, one which is responsive simply to the magnitudes of the first two received pulses, to yield the message unambiguously. Thus in the following example, the receiver 6 lies somewhere in the disc-shaped volume 8 which has been, more or less, arbitrarily sub-divided into two sub-regions, viz.:

H/15 x H (short range) and H x H (long range), and

For simplicity, signalling in deep water, H =2500 fathoms, under isovelocity water conditions is considered.

For the case where the receiver is known to be at short (long) range, submerged somewhere between (100', 1000), what are the limits on detonation depth so that the first two pulse arrivals will unambiguously yield the message. The useful message/depth dictionary will be abridged, since the messages are no longer to be associated with arbitrary depth zgH, but must now be culled from the z region subject to the condition that the reflected pulses do not overlap the time interval T between the direct, main pressure shock wave pulse (hereinafter called the main bang) and the first bubble pulse.

Since the receiver has been constrained to be above 1000, rapid calculation shows that the bottom reflected pulse will be non-overlapping except for z-H and x H, e.g., for x=5H and z=0.9H, the time interval between the arrival of the main bang and its bottom reflection, T will be approximately 100 milliseconds; however, since T at this great depth is approximately in the order of 1 millisecond, there is no danger of confusing the bottom reflection of the main bang with the direct bubble pulse. Therefore, at worst, a very small region of the z axis near the bottom may have to be excluded.

If the interference from the surface reflected pulse is to be circumvented, the problem is somewhat more difficult. Examination of FIG. 3 shows that the curve 3, corresponding to receiver coordinates (x=H, y=100'), and curve 5 (x=1000, y=1000'), bound assumed short range receiver positions. In order to avoid the surface reflected pulse, either all z 130' or all z 1600 are to be excluded. In other words, unambiguous messages can be selected from either the upper layers, z l30', or the lower layers, z 1600, but not both. Curves similar to 3 and 5 can be drawn for the long range case as well.

FIGS. 2, 4 and 5 illustrate a representative underwater communication system following the principles of the invention, comprising a transmitting station 2, a transmitter 4, and a receiver 6. The transmitting station 2 ordinarily consists of a ship or an aircraft. The transmitting station 2 drops the transmitter 4 in free fall, propels it downward as an artillery shell, or causes it to propel itself downward by means of a rocket motor. In accordance with aforementioned conditions, the receiver(s) 6 are constrained to occupy the disc-shaped volume 8.

A simple application of the system will be described in detail to demonstrate the basic principles. For definiteness, let a receiver 6 be at a horizontal range x=H and at a depth y=1000'. The lower layer of z is chosen to supply the message set 10. The vertical z axis through the transmitting station 2 acts as the axis of the unambiguous message receiving volume 8. As the transmitting station 2 moves, so does the region 8. When a message or command from a predetermined vocabulary is to be sent, the sender first consults the predetermined message/depth dictionary and then sets the detonating depth of the hydrostatic fuse 12 accordingly. The transmitter 4 is then dropped. When it reaches the depth corresponding to the preset hydrostatic pressure, the hydrostatic fuse 12 detonates the explosive charge 14. The main bang and first bubble pulse radiate omnidirectionally from the transmitter 4, separated in time by T seconds as per equation for T FIG. 1 shows the pressure vs.

time diagram of a 2 pound TNT charge detonated at depth z=12 kilofeet as recorded by a. blast gauge located at horizontal distance x=10 kiloyards and depth this example was discussed by D. Epstein, J. Acous. Soc. Am., 35, p. 800 (1963). FIG. 2 illustrates the case for a two-ounce charge of TNT detonated at z=12 kilofeet and a receiver 6 located at x=H, y=1000'. Also shown are the direct ray 16, the first bottom bounce ray 18, and the first surface reflected ray 20. The receiver 6 picks up the pressure pulsations via the hydrophone 21, measures the time difference, T and reads out the associated message. The heart of said receiver is in the electronic-amplifier/signal processing/ decoder unit 22. Should the message require action on the part of this particular receiver, such action would be taken by the display/actuator unit 24.

In the next example to be given, FIGS. 2, 4, 5 and 6 illustrate a representative communication system following the principles of the invention, as before, except that the receiver 6 amplifier/ decoder unit 22 is more sophisticated than the one used in the previous example. One of the principal features of 22 is its ability to respond only to positive pressure pulsations. It is a well known fact that surface reflected pressure pulses suffer a phase inversion. Since the receiver will now only respond to positive pulsations, ambiguities introduced by the surface reflected ray 20 are circumvented; therefore much of the heretofore excluded detonation regions are eliminated. To prevent the receiver from responding more than once to the same message, i.e., responding to the direct pulse pair, via ray 16, and the bottom reflected pulse pair, via ray 18 (for the case illustrated where only the one-bounce reflections are of significance), a refractory period (time during which receiver 6 will not respond to any further stimuli) is designed into unit 22.

The presently preferred embodiment of the receiver/ decoder unit 22 of the receiver 6 is shown in FIG. 6'. In its simplest sense, the electrical replica of the direct ray 16 main bang pressure pulse from hydrophone 21 arrives at the input of the amplifier 28 at random time t The amplified main bang pulse '7 is fed to the input of a trigger circuit 30, e.g., the well-known Schmitt trigger. A variable and/ or presettable positive voltage 32 constituting a threshold is also fed into the input of 30; when the main bang pulse exceeds the threshold (set in accordance with any one of a number of well known statistical hypothesis testing schemes to give the allowable false alarm and missed alert probabilities in the presence of noise) a sharp positive pulse of fixed magnitude and duration appears at the output of 30, precisely establishing time t This positive output pulse is fed to one input of the and gate 33. Since a positive voltage presently exists at the other input to 33, fed from the T1 output of the refractory time monostable flip-flop 34, the sharp positive pulse passes through 33 to the transfer input, T, of the bistable flip-flop 36. Since 36 is presently in the reset position, the

Q output of 36 makes a rapid transition from the 0 mode (say, zero volts) to the 1 mode (say, a fixed positive Voltage) thereby firstly impressing a positive step voltage at the input of the differentiating network 48 which in turn outputs a sharp positive pulse to reset pulse counter 40 v1a or gate 50, and secondly synchronizes and gates out the output of the clock 38. The output of digital clock 38 is a train of sharp positive pulses. The required clock rate is a function of the dictionary size, water depth,'hydrostatic fuze dynamic range, accuracy and resolving power, and the type and weight of explosive charge. If, say, a dictionary of messages is desired, for the case in point, a clock rate of 100 kilocycles/second should do. The train of clock pulses, initiated by the main bang and terminated by the first bubble pulse, is fed to the input of the counter or finite-state-machine 40 which would consist of say, 14 binary memory stages yielding different possible combinations. The binary stage outputs of 40 go to the inputs of the decoder matrix 42. The output lines of 42 are sent to one input of the set of dual input and gates 44. Each dual input gate of the set 44 also receives an input from the 6 (not Q) output line of 36. Therefore, the set of and gates 44 will not permit readout until the entire message has been read-in; furthermore, counter 40 will memorize the message and and gates 44 will continue to read-out same until such time as another main bang 7 is received, heralding the advent of another message, or counter 40 is cleared. The outputs of and gate set 44 go to the inputs of the actuator/ display unit 24. As soon as the first bubble pulse 9 arrives, at time T it is amplified, detected, and causes bistable flip-flop 36 to switch modes. The Q output of the bistable flip-flop 36 goes from 1" to 0 terminating the count; the 6 output goes from O to 1 thereby gating the message from decoder matrix 42 to the actuator/ display unit 24 via the set of and gates 44. The positive step voltage created when 6 goes from 0 to 1 is differentiated by the differentiating network 46 which operates upon the rising leading edge of voltage thereby outputting a sharp positive pulse. This positive pulse triggers the input of the refractory time monostable flip-flop 34 so that its Q output goes from 1 to O. This action inhibits transmission of signals through gate 33 for the duration of the refractory time.

The arrival of another main bag, subsequent to the refractory time, causes the Q outputof bistable flip-flop 36 to go from 0 to 1, as before. The resulting positive step voltage is also fed to the input of differentiating network 48 and the ensuing positive spike is fed to one of the inputs of the or gate 50. The resulting output spike of or gate 50 is fed to the reset, R, input of counter 40, clearing the previous message and preparing counter 40 for the new message.

Should a noise pulse exceed the threshold and inadvertently start the clock, unless another noise pulse exceeds the threshold within the order of time of the expected duration of the bubble pulse interval, the counter 40 will overflow. A sharp positive pulse will emanate from the overflow output, 0, of the counter 40 and be fed to one of the inputs of the or gate 52 and thence to the reset, R, inputs of bistable flip-flop 36 and pulse counter 40.

A manual reset push-button 54 is provided for manual reset of the receiver unit 6. It feeds the or gate 52. Electrical power for the receiver is supplied by the power supply 56.

MODES OF OPERATION It is quite apparent that this invention may be embodied and used in many forms.

It may utilize single hydrophones or hydrophone arrays, signals may be detected and decoded in the time domain as shown in the presently preferred embodiment or in the frequency domain, and communication can be oneway or two-way. Submarines, for example, can signal to each other or to surface vessels by propelling the explosive transmitter upwards or downwards as required.

If there are M possible messages and R receivers and only one receiver, say, is to respond, then an addressing function is required. In its crudest sense, only M/R information messages (on the average) would be available. The total number of discrete messages could be greatly increased by using two or more explosive transmitters per message, i.e., the total number of different messages would now be M where N=number of explosive transmitters. (If M=1OO and N=2, M =l0,000.) Receiver unit 6 would have to be modified for this mode of operation.

Frog-men could communicate by carrying a number of small explosive transmitters 4 and a microminiaturized portable version of the receiver 6 shown in FIG. 6. Its physical embodiment would be similar in construction to that of the electric wrist watch shown in the diagrams on the lower half of page 16 of Electronic Design 12, No. 1, (1964). The face and hands of the wrist watch perform the functions of the counter 40,. the matrix 42, and the display unit 24. The basic frequency of operation of the wrist watch would be changed from its present frequency of 360 c.p.s. to, say, kc. and the clock would be gated by flip-flop 36 as before. The time indicated on the face of the wrist watch would then correspond to the number of the message received.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claims.

We claim:

1. A method of effecting transmission of intelligence in an underwater milieu comprising the steps of displacing an explosive charge to a preselected depth level beneath the water surface in accordance with the nature of the quantum of intelligence to be transmitted,

detonating said explosive charge at said preselected level to generate an explosive pulse spaced a predetermined time interval from its attendant first bubble pulse, and measuring the duration of said time interval at a location remote from said explosion, said time interval being selectively representative of the nature of the quantum of intelligence desired to be transmitted.

2. An underwater intelligence transmitting system wherein desired quanta of intelligence is represented by the time interval intermediate underwater detonation of an explosive charge and the first bubble pulse resulting therefrom comprising an explosive charge of preselected composition and weight,

means for displacing said charge from a point of release thereof to a preselected depth beneath the water surface,

hydrostatic fuz means responsive to the presence of said charge at said preselected depth for effecting detonation of said charge,

sensing means responsive to the receipt of water traversable pressure pulses for converting the same into electrical impulses representative thereof,

means for measuring the duration of the time interval between the receipt of the pressure pulse resulting from the detonation of said charge and from the first bubble pulse attendant therewith,

and means responsive to the duration of said time interval for converting the same into an indicia of recognizable intelligence.

3. A receiver assembly for an underwater intelligence transmitting system wherein predetermined quanta of intelligence are represented by the duration of the time intervals intermediate detonation of explosive charges and the first bubble pulses resulting therefrom, comprising sensing means responsive to the receipt of water traversable pressure pulses for converting the same into electrical impulses selectively representative thereof,

triggering means responsive to receipt of an electrical impulse representative of a positive pressure pulse generated by a remote underwater detonation of a single explosive charge and having an amplitude greater than a predetermined threshold value for initiating a sensory timing period of predetermined maximum permissible duration.

means responsive to the receipt of the first positive pressure bubble pulse resulting from the detonation of said single explosive charge by said sensing means and after initiation of said sensory timing period for terminating said sensory timing period prior to the maximum permissible duration thereof,

means responsive to the duration of said sensory timing period for converting the same into an indicia of OTHER REFERENCES recognizable intenigenqe and means r.esponsive.to the Leroy et 211.: Some Acoustical Characteristics of Unexpiration of maxupum permisslblej duratlon derwater Explosions of Hydrogen-Oxygen Mixtures, i sensory Penfd Y i i fi of i532? Journal of the Acoustical Society of America, vol. 35,

we ressure u e u se crew in or an icanpresettin Said erin means 5 No. 2, February 1963, pp. 245 and 249 rehed on.

y g gg g Paramonov: Deep Sea Research, vol. 10, No. /2, Jan- References Cited nary-April 1963, pp. 77-81 relied on.

UNITED STATES PATENTS RICHARD A. FARLEY, Primary Examiner 2,587,301 2/1952 Ewing 340-6 10 2,665,410 1/1954 Burbeck 32468 3,141,960 7/1964 Biser 3403 X 181-.5; 3403 

2. AN UNDERWATER INTELLIGENCE TRANSMITTING SYSTEM WHEREIN DESIRED QUANTA OF INTELLIGENCE IS REPRESENTED BY THE TIME INTERVAL INTERMEDIATE UNDERWATER DETONATION OF AN EXPLOSIVE CHARGE AND THE FIRST BUBBLE PULSE RESULTING THEREFROM COMPRISING AN EXPLOSIVE CHARGE OF PRESELECTED COMPOSITION AND WEIGHT, MEANS FOR DISPLACING SAID CHARGE FROM A POINT OF RELEASE THEREOF TO A PRESELECTED DEPTH BENEATH THE WATER SURFACE, HYDROSTATIC FUZE'' MEANS RESPONSIVE TO THE PRESENCE OF SAID CHARGE AT SAID PRESELECTED DEPTH FOR EFFECTING DETONATION OF SAID CHARGE, SENSING MEANS RESPONSIVE TO THE RECEIPT OF WATER TRAVERSABLE PRESSURE PULSES FOR CONVERTING THE SAME INTO ELECTRICAL IMPULSES REPRESENTATIVE THEREOF, MEANS FOR MEASURING THE DURATION OF THE TIME INTERVAL BETWEEN THE RECEIPT OF THE PRESSURE PULSE RESULTING FROM THE DETONATION OF SAID CHARGE AND FROM THE FIRST BUBBLE PULSE ATTENDANT THEREWITH, AND MEANS RESPONSIVE TO THE DURATION OF SAID TIME INTERVAL FOR CONVERTING THE SAME INTO AN INDICIA OF RECOGNIZABLE INTELLIGENCE. 